The previous engine management systems developed by Transcom Gas Technologies Pty Ltd, such as that described in PCT/AU93/00649 (WO94/13946), employed a stepper motor based throttle actuator coupled via a gear box and linkages to a throttle valve. This mechanism proved to be unreliable and inaccurate due to the lack of feedback. The inaccuracy of this mechanism was further exacerbated by the open loop control strategies employed by the previous control systems, which required repeatable positioning of the valve. Furthermore, the complete stepper motor, gearbox and throttle valve assembly was bulky and connected via adjustable linkages which if varied affected the engine tuning.
This prior art stepper motor throttle actuator achieved variable resolutions using a lever and linkage mechanism. The transfer function between the number of 1.8.degree. stepper motor steps and throttle valve angle gave extremely high resolution at low step numbers which correspond to the engine's idle setting, where the greatest control is required. The step number at idle was approximately 30, while the throttle angle difference between step 30 and 31 was 0.000956 radians. The throttle travels through 1.202835 radians between its fully open and fully closed positions. Therefore the number of steps required to achieve the same resolution at idle for a fixed resolution is at least 1258 (1.202835/0.000956) steps.